In a high dynamic environment (aerospace field, launch vehicles, satellites and missiles), a GPS receiver is in a high-speed movement state and may have a very large acceleration or a jerk, and general commercial GPS receivers cannot work normally. In the high dynamic environment, a higher movement speed of a receiver enables a larger Doppler frequency shift to exist on a carrier, and furthermore when the receiver changes the movement state in a very high acceleration or a jerk, a violent change in the Doppler frequency shift of the carrier will be caused. The Doppler frequency shift with a violent change caused by high dynamism may bring about some problems to a tracking loop of the GPS receiver:
(1) it is required to complete an acquisition process as soon as possible and enter into a tracking process, and too large Doppler frequency shift may bring about a great difficulty to initial tracking, and in this situation, the tracking loop may only use a frequency-locked loop or a phase-locked loop with a wider bandwidth;
(2) since the Doppler frequency shift changes violently, an integration time must be very short, otherwise, a tracking bandwidth of the phase-locked loop or the frequency-locked loop may be easily exceeded, thus causing losing lock of signals;
and (3) when the signals are tracked in the high dynamic environment, since the Doppler frequency shift of the carrier changes violently, a shorter integration time and a larger filter noise bandwidth are used, and therefore, a loop signal to noise ratio is generally lower, and the tracking precision is poorer.
It is well-known that in GPS receivers, compared with traditional scalar tracking loops (STL), vector tracking loops (VTL) have many advantages, and particularly in weal signals and high dynamic environments, VTLs have better tracking sensitivity and re-acquiring velocity. The traditional GPS receivers may work well when the signal to noise ratio of a GPS signal is higher and dynamism of the carrier is lower. However, when being in a high dynamic movement state or the signal to noise ratio of the GPS signal is lower, the traditional GPS receiver will lose locking of the GPS signal. On the contrary, a GPS receiver based on a vector tracking loop has a much higher tolerance capability on a low signal to noise ratio and high dynamic environment than that of the traditional GPS receiver, and the vector tracking GPS receiver has a better performance than that of the traditional receiver.
However, a traditional vector tracking technology does not take full use of internal relations of the signals in each channel, and cannot be called vector tracking in a real sense. In fact, apart from pseudo ranges and pseudo range rates of the signals in each channel having internal coupling, phase discriminator outputs (pseudo ranges and pseudo range rate residuals) of all channels are also not independent from each other. When processing weak signals, we can also utilize this internal relation so as to improve the performance or the GPS receiver.
The present invention provides a new vector tracking strategy on the basis of a vector tracking idea to further improve the performance of the vector tracking GPS receiver. In a new vector tracking strategy design, a phase discriminator/a frequency discriminator in a traditional vector tracking loop is discarded, and baseband signals of visible satellites in each channel are taken as an observation value after performing non-coherent integration, and EKF is used to estimate the observation value so as to directly solve the position, the velocity, a clock error, etc. of the GPS receiver. Because of the existence of non-coherent integral calculation, when GPS satellite signals are relatively weak, a carrier to noise ratio of an observation quantity may be effectively improved, and the tracking sensitivity is improved.